A polymer thermolysis method (Patent Citations 1 and 2) is known as a method for obtaining a graphite film excellent in electric conductivity and heat conductivity. In the polymer thermolysis method, a heating treatment is given to a polymeric film under (i) an inert atmosphere such as argon or helium, and/or (ii) reduced pressure. An example of such a polymeric film is a film made of polyoxadiazole, polyimide, polyphenylenevinylene, polybenzimidazole, polybenzoxazole, polythiazole, polyamide, or the like.
Meanwhile, a method (described in Patent citation 3) is known as a mass-production method for producing, with high productivity, a large volume of graphite for use in a shaft bearing, a seal, a melting pot, a heating element, and the like. In the method, a mixture of (i) carbon-source powder as coax, from which carbon is obtained and (ii) a caking additive such as tar pitch is sintered, and then the sintered substance, i.e., the mixture thus sintered, is electrified and heated, with the result that graphite is obtained. The electric conductivity and heat conductivity of the graphite thus produced are inferior to those of the graphite produced by using the polymer thermolysis method.    Patent Citation 1: Japanese Unexamined Patent Application Publication Tokukaisho 60-181129    Patent Citation 2: Japanese Unexamined Patent Application Publication Tokukaihei 61-275116    Patent Citation 3: Japanese Unexamined Patent Application Publication Tokukaihei 5-78111However, the heat conductivity of such conventional graphite obtained by heating a polymeric film under an inert atmosphere and/or reduced pressure was found to be insufficient, so that the graphite was insufficient as a heat radiation material for use in a recent electronic device emitting a drastically large amount of heat.
For a better heat radiating property, the thickness of the graphite may be thicker to attain a greater heat transport. However, in the conventional polymer thermolysis method, damage to the film is easily caused. Even if the film was produced without damage, graphite thus obtained would have a low heat conductivity. A reason of this is as follows. In the polymer thermolysis method in which the heating is carried out under the inert atmosphere, the raw material film is heated from its surface, so that graphitization progressed unevenly between the inside of the film and the surface thereof. As a result, the film attains merely a low overall heat conductivity.
On the other hand, in the polymer thermolysis method in which the heating is carried out under the reduced pressure, the raw material film was heated by (i) heat conducted via a contact portion thereof with a heater and (ii) radiant heat from a heater. However, with such heating, the raw material film is heated unevenly, so that graphitization progressed unevenly. This results in a low heat conductivity of the film.
Further, due to the graphitization progressing from the surface of the raw material film, it is difficult for decomposition gas to get out from the inside of the raw material film, especially in cases where the raw material film is a thick one. The decomposition gas emitted out therefrom with such difficulty causes damages to the film. Even in cases where the film was not broken, graphitization does not progress sufficiently in the inside of the film as compared with that in a thin film. Thus, the film has a heat conductivity much inferior to that of the thin film.
Meanwhile, in the conventional method for obtaining graphite by electrifying and heating a sintered substance made from a carbon-source powder and a caking additive, the sintered substance is used as a raw material. The electric conductivity of the sintered substance is uneven, so that a current unevenly flew in the sintered substance. Accordingly, temperature rose locally therein, with the result that the sintered substance is graphitized unevenly and therefore is cracked and broken with ease. Therefore, the graphite thus obtained by using this conventional method has heat conductivity and electric conductivity much inferior to those of the graphite film obtained by heating the polymeric film.
Further, in production of a plurality of sintered substances, displacement of sintered substances likely occur during heating. Such displacement would deteriorate properties thereof. Proposed to prevent the deterioration of the properties is such a method that the sintered substances are adhered by an adhesive agent and then are electrified and heated. With this, graphite having no crack can be obtained but the graphite has much inferior heat conductivity and electric conductivity.
Moreover, when the method of fixing raw material films with an adhesive agent is adopted for acquirement of graphite in the form of a plurality of films, the adhesive agent causes deterioration of quality of the graphite. Thus, the method is not preferable.